Certain stages of semiconductor manufacturing require thermal cycling of a semiconductor substrate, wherein the substrate is repeatedly heated and then cooled. For example, each photoresist processing stage of semiconductor manufacturing requires a heating, or baking, step to flow the photoresist material along the substrate surface, followed by a cooling step to set the photoresist. In order to produce high quality substrates suitable for state of the art integrated circuit applications, the temperature of a substrate during thermal cycling must be precisely controlled with respect to both temporal temperature profile and temperature uniformity across the substrate.
Conventional heaters typically employ resistive heating elements that are bonded/brazed to heat conduction plates, and/or employ integrated bake and chill plates having a plurality of cooling fluid channels and microchannels to affect cooling as described in commonly assigned U.S. patent application Ser. No. 08/939,926 filed Sep. 29, 1997. As a result of stresses introduced by repeatedly heating and cooling a heat conduction plate, delamination of bonded/brazed resistive heating elements can occur, requiring process downtime during heater replacement and generating safety concerns due to broken wires and/or open circuits. Further, the use of microchannels to affect cooling increases heater manufacturing costs and thus the cost per wafer processed.
Accordingly, it is an object of the present invention to provide an improved heater apparatus which can withstand repeated thermal cycling and that is easily manufacturable.